Recombinant DNA techniques will be developed and applied to the study of genetic regulatory elements in prokaryotes (phage Lambda) and eukaryotes (mouse). To further our understanding of the mechanisms by which DNA replication is initiated the interaction between phage Lambda's replication initiator protein (gene O product) and its binding site in DNA (the origin of replication) will be analyzed by protection methods. The O protein will be prepared in sufficient quantities to begin examination by X-ray crystallography. In the mouse the genetic basis for control of immune responses will be studied in both B cell and T cell systems. In B cells the focus will be on Immunoglobulin D and its baroque regulation. In T Cells the genes controlling T cell surface molecules I-J and Iat will be cloned and subjected to structural analysis at the DNA level. A new method for cloning of cDNA molecules will be developed that allows efficient cloning of RNA molecules that are highly purified by subtractive hybridization. The cloned molecules will be identified by antibody screening in a triple phase expression vector.